Technical Abstract:
Full understanding of the control of plant carbon and nitrogen metabolism involves knowledge of all the biological mechanisms that determine the cellular and subcellular content of each protein as well as their enzymatic activity. One major way in which enzyme activity can be regulated involves post-translational modification of the protein, and one of the most important mechanisms involves attaching phosphate molecules to proteins at specific positions in a process known as protein phosphorylation. This mechanism is known to regulate important enzymes in sucrose metabolism and nitrate assimilation. Protein phosphorylation is catalyzed by enzymes known as protein kinases that recognize the sites where phosphate will be attached based on amino acid sequence patterns. Some of these patterns can be modified by reactive oxygen species, which are produced in plants as unintentional byproducts of aerobic metabolism and also as intentional products to serve as signaling molecules. We speculate that this may be an important, but presently unrecognized, mechanism to link oxidative signals with changes in protein phosphorylation.